Analysis

Frank GardnerBBC security correspondent

Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday. That is when David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers. It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert.

Any military response, if it's decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean. US vessels there are reported to have about 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles.

But Russia, Syria and Iran have all issued strong warnings against any western military action.

In his phone call with the Russian president, Downing Street said, Mr Cameron and Mr Putin "both reiterated the position agreed by all leaders at the G8 in June: no-one should use chemical weapons and any use would merit a serious response from the international community".

A spokesman said Mr Cameron told Mr Putin "there was no evidence to suggest that the opposition had the capability to carry out such a significant attack, and the regime had launched a heavy offensive in the area in the days before and after the incident".

The Syrian regime "had also prevented UN access in the immediate aftermath, suggesting they had something to hide".

Mr Putin, though, said they did not have evidence of whether a chemical weapons attack had taken place or who was responsible, the spokesman said.

Russia has warned strongly against Western military action against Syria.

On Monday, Russian Foreign Minister Sergei Lavrov said any intervention in Syria without a UN mandate would be a "grave violation of international law".

The UN Security Council is made up of 15 members including five permanent members - China, Russia, France, the US and the UK - who have the power to veto any resolution.

UK Foreign Secretary William Hague earlier told the BBC it would be possible for the UK and its allies to respond without the UN's unanimous backing.

Mr Hague said a response could be "based on great humanitarian need and distress".

"We, the United States, many other countries including France, are clear that we can't allow the idea in the 21st Century that chemical weapons can be used with impunity," he said.

Parliament recall

Mr Cameron is to chair a meeting of the National Security Council - attended by military and intelligence chiefs and senior ministers - on Wednesday to discuss potential responses.

Downing Street said the government would decide on Tuesday "whether the timetable for our response means it will be necessary to recall MPs sooner than Monday when the House is currently due to return".

“Start Quote

Let's see the evidence - let's base our decisions on hard evidence”

End QuoteJohn Baron MPForeign Affairs Select Committee

Meanwhile, former UK special representative for the Middle East, Lord Williams, said that, although Mr Kerry and Mr Hague "may say there's compelling evidence" the Syrian regime had used chemical weapons, "this is yet to be proven to the general public".

"And, of course, against a background of the Iraq war, there will be misgivings," he told BBC News.

He said UN inspectors in Syria must "be given some time to make sure that their view is or is not that chemical weapons were used and that the authors of that chemical attack was indeed the government".

And Tory MP John Baron, a member of the Foreign Affairs Select Committee and a former army captain, said a "slightly sceptical" Parliament must be consulted about any possible UK military intervention.

"Parliament was told that Saddam had weapons of mass destruction," he said.

"We were told that we'd be in and out of Helmand without firing a shot. We're now being told that Assad's used chemical weapons."

Labour's shadow foreign secretary Douglas Alexander has also said he would "expect the prime minister to make his case to Parliament" before a decision was made about UK involvement in military action.

Please turn on JavaScript. Media requires JavaScript to play.

It is understood the most likely military response to the suspected chemical weapons attack would be a one-off or limited guided missile strikes on Syrian military targets fired from US Navy warships, says BBC security correspondent Frank Gardner.

In Syria, the rebels say Syrian President Bashar al-Assad's regime carried out a chemical attack, but the regime blames rebel forces - saying footage of the attack was "fabricated".

UN chemical weapons inspectors visited five sites around Damascus on Monday, although their trip was delayed when their convoy came under sniper attack.

They went to hospitals, interviewed witnesses, survivors and doctors, and collected some samples, UN Secretary General Ban Ki Moon said.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.